WITTGEN AB (1961) Oölogische nidologische and communications, 1959-II and 1960. Early brood of black-necked grebe Podiceps nigricollis. LIMOSA 34 (3): 264-264.
Black-necked Grebe Podiceps nigricollis Early brood of black-necked grebe Podiceps nigricollis
